Video streaming, data streaming, and broadband digital broadcast programming are increasing in popularity in wireless network applications, e.g., Internet Protocol (IP) multicast services. To support these wireless applications, wireless broadcast systems transmit data content that support data services to many wireless terminals simultaneously. Digital media content or other data is broadcasted using various application protocols, transport protocols and network protocols. For example, a broadcast system provides IP data broadcast where audio-visual service is transmitted so that MPEG4-AVC video, MPEG4-AAC audio and auxiliary data components are packetized and encapsulated to RTP and/or ALC. The packets are subsequently formatted to UDP and IP and transmitted over MPE in MPEG2-TS (for example DVB-H). In a packet-switched domain, the concept of a multi-media session may require that one or more session components (audio, video and auxiliary data in above case) are logically bound together. The portions of the multi-media session are sent between a common start time and end time. However, with a broadcast environment all receivers that are able to receive the broadcast signal can receive the data carried by the broadcast signal. It is important that the content seller limits access to multi-media content so that only entitled receivers can present the multi-media content to users.
Digital Rights Management (DRM) systems, like Open Mobile Alliance (OMA) DRM system, are being used for selling access to discrete files, like OMA DRM Digital Content Files (DCF). As one possible solution, a device (as instructed by its human user) from a Content Provider obtains the DCF (e.g. an MP3 music file), which is encrypted by a content key. The device separately obtains (i.e. purchases) from a Rights Issuer (RI) a Rights Object (RO) that may include (among other things) two parts: the content key for decrypting the DCF, and usage rights for the DCF. Usage rights control the way in which the device (and thus its human user) may use the decrypted DCF content; for instance, time limits for using the content, whether the content may be copied, etcetera. Different RIs may sell ROs for the same DCF at different prices and with different usage rights.
Often, e.g. in the case of OMA DRM, usage rights are expressed in a Rights Expression Language (REL) which may contain conditionality based on variables like days of week, time of day, period of days, etc. . . . For example, it may be stated that a particular usage right extends for a period of time. Examples of REL include Open Digital Rights Language (ODRL) and eXtensible rights Markup Language (XrML).
Recently, DRM systems are being deployed for selling streaming services, too, in addition to discrete DCF files. A special case of such streaming services is true radio broadcast streaming services (broadcast services hereinafter), where multiple devices receive the same broadcast stream. For instance OMA DRM has been suggested for selling and purchasing IP datacast (IPDC) services, and the solution is being standardized by the Digital Video Broadcasting (DVB) organization, in order to (among other things) support handheld television receivers on top of DVB-H (handheld) radio broadcast technology.
Typical organizational roles in broadcast services include: 1) a broadcaster who obtains the streaming content from content providers and broadcasts it encrypted over the radio path, and 2) multiple RIs, who sell ROs for decrypting the content and setting the usage rights for it in the devices receiving the broadcast. The ROs may be delivered over the same broadcast radio path as the encrypted content itself, or via separate interaction channels such as cellular data carriers (e.g. GSM GPRS, General Packet Radio Service).
In such a scenario, it is typically not feasible for the key in each RO to decrypt the streaming content directly, since the streaming content is continuous (unlike discrete DCF files). One known technique of content decryption is a key hierarchy such as is used in DVB conditional access. Broadcaster sends sequences of streaming content each encrypted by a traffic key (TK), periodically changing the traffic key. At least whenever the traffic key changes, a Key Stream Message (KSM) is sent, containing the traffic key encrypted by a service key (SK). The ROs contain the service key. Therefore, receiving devices may use the service key in the ROs to decrypt the traffic keys in the KSMs. The receiving devices may then use the traffic keys to decrypt the streaming content. In practice, the KSMs must be broadcast very frequently so as to enable quick “channel switch” from one service to another.
The service key also changes periodically, although the frequency of change is typically much lower. A new service key is then required for the device to continue to decrypt the streaming content. Therefore, a new RO with the new service key may be obtained by devices to replace old ones. Accordingly, ROs have a certain validity period, which equals the time during which the service key can be used to decrypt the traffic keys so as to decrypt the streaming content.
As specified above, a RO for a broadcast service serves to decrypt and make accessible streaming content, for the validity period of the RO. Like in the DCF case, the RO can also be used to state usage rights expressed in REL for the same validity period. As an example, consider the DVB-H based handheld television broadcast service. Typically devices are allowed to render on a display (so that a human user may view) the television service, such as a program on a channel, as it is received. Usage rights may state what the device/user may do with the streaming content, which may be the television service. For example, the usage rights may provide that the content may be recorded, may be played back at a later time, may be copied to another device, may only be viewed or whatever rights are desired to be provided.
While this methodology provides a certain level of functionality, there is a problem. Each RO can only state one set of usage rights for the validity period. This level of control may be insufficient. For example, there may be different types of television programs in a handheld television broadcast service that the RIs may wish to provide different levels of control regarding usage. The RIs may wish to allow a liberal “do anything” usage rights for certain types or portions of content such news, advertisements or quizzes but restrict usage rights for other types or portions of content such as premium sporting events or feature movies. Thus, while ROs with relatively long validity periods are fine for streaming content access (i.e. decryption), it would be useful to provide a more fine grained means of providing usage rights with increased frequency and/or precision within the validity period of the RO so that the usage of the type or portion of the content is in accordance with the usage rights intended to be granted for the type or portion of content.
Furthermore, rights to certain content may vary depending on the time of day or the day of the week. In addition, a user may have different rights for different portions of the content. For example, in order to enhance revenue collections, a user is often permitted to access premium multi-media services only if the user subscribes to the service or orders the service (e.g., pay per view). However, the content may also be separated into time periods. Thus, for example, a user may decide to subscribe to a weekend edition rather than a full week subscription. The RIs may wish to allow some of the content available in the weekend edition subscription to be saved and forwarded freely to others while limiting other portions of the content to a single use or to a more controlled distribution set.